PbO as an efficient and reusable catalyst for one-pot synthesis of tetrahydro benzo pyrans and benzylidene malonitriles
ASHOK V BORHADEa,∗, BHAGWAT K UPHADEb and DIPAK R TOPEa
aDepartment of Chemistry, Research Center, HPT Arts and RYK Science College, Nashik 422 005, India
bDepartment of Chemistry, Research Center, PVP College, Pravaranagar (Loni Kd) 413 713, India e-mail: ashokborhade2007@yahoo.co.in
MS received 18 January 2012; revised 11 October 2012; accepted 17 October 2012
Abstract. PbO nanoparticles have been employed as an efficient catalyst for the solvent-free synthesis of tetrahydrobenzo pyrans (yields 81–91%) and benzylidene malonitriles (yields 90–96%) at room temperature using green chemistry approach. PbO nanoparticles were found to be highly efficient, eco-friendly and recy- clable heterogeneous catalyst. PbO nanoparticles were prepared by hydrothermal method and characterized by IR, XRD, BET Surface area, SEM, EDAX and TEM with SAED techniques.
Keywords. PbO nanoparticles; tetrahydrobenzo pyrans; benzylidene malonitriles; grinding; solvent-free.
1. Introduction
Benzopyrans and their derivatives are known to show several pharmacological properties such as spas- molytic, diuretic, antianaphylactin, antisterility and are used as anticancer agents.1The polyfunctionalized ben- zopyrans are also used as cosmetics, pigments and biodegradable agrochemicals.2 The benzylidene malo- nitrile derivatives have been found to posses inhibitory activity to HER2,3EGFR,4IGF1R5and have been used for treatment of cancer.6 Many synthetic procedures have been reported for tetrahydro benzo pyrans and benzylidene malonitriles.
The tetrahydro benzo pyrans have been previ- ously synthesized by two or three-component con- densations including the use of catalysts like potas- sium phosphate,7ZnO-beta zeolite,8 Ce(SO4)2.4H2O,9 s-proline,10caro’s acid-silica gel,11hexadecyl trimethyl ammonium bromide,12 sulphonic acid functional- ized silica,13 tetra butyl ammonium bromide,14 rare earth perfluorooctanoate,15 basic quaternary ammonium salt,16 phenyl boronic acid,17 LiBr,18 TEAA,19 PEG- 400,20basic ionic liquid,21amines22and (NH4)2HPO4.23 The benzylidene malonitriles were synthesized using catalysts such as calcium oxide,24 TEBA,25 PEG,26 base,27 NH2SO3NH4,28 MgBr2.OEt2,29 organo-base mediation,30 quaternary ammonium salts,31 Na2S/
Al2O3,32 mpg-C3N4,33 mesoporous base,34 zirconia,35 amine supported on silica gel36and MgC2O4/SiO2.37
∗For correspondence
Recently, metal oxide nanoparticles in the form of na- nocatalyst have emerged as viable alternatives to con- ventional materials in various fields of chemistry and attracted marvelous interest of chemists. Metal oxide nanoparticles are known to be promising heteroge- neous catalysts in a variety of organic transforma- tions.38 Nanoparticles have the potential for impro- ving the efficiency, selectivity and yield of catalytic processes. In particular, the PbO nanoparticles provide higher surface to volume ratio in the reaction. Higher selectivity of PbO nanoparticles towards reaction pro- ceeds through less waste and fewer impurities, which could lead to safer technique and reduced environmen- tal impact. PbO nanoparticles have been investigated as catalysts in the organic reactions including the Paal–
Knorr reaction and oxidative coupling of methane.39,40 Thus, the significant catalytic property with opera- tional simplicity, high reactivity, environmental friend- liness, reduced reaction times and reusability of PbO nanoparticles have prompted us to employ as catalyst for multicomponent reaction.
In view of the importance of PbO nanoparticles as a catalyst in organic synthesis, we report here a simple solvent-free synthesis of tetrahydrobenzo pyrans and benzylidene malonitriles. In this study, PbO nanopar- ticles were synthesized by hydrothermal method and characterized by IR, XRD, BET Surface area, SEM, EDAX and TEM with SAED techniques. In view of emerging importance of heterogeneous catalyst, we wish to explore the applications of PbO nanoparticles as a catalyst in organic synthesis.
583
2. Experimental
The synthesized PbO nanoparticles were character- ized by FTIR using Shimadzu 8400 s instrument. XRD pattern was recorded using Phillips-1710 diffractome- ter with Cu–kα radiation (λ = 1.54 Å). The surface area was recorded with the help of Quantachrome Autosorb Automated Gas Sorption System. SEM and EDAX were recorded using JEOL-JEM-6360 micro- scope. TEM was recorded with SAED using CM-200 Philips Microscope. Melting points were determined using open capillary tubes on Veego melting point appa- ratus and are uncorrected. FTIR spectra were recorded on Shimadzu 8400 s spectrometer using KBr pellets.1H NMR spectra were recorded on a Bruker Advance II 400 MHz spectrometer in DMSO-d6 with TMS as an internal standard.
2.1 Synthesis of PbO nanoparticles
A mixture of citric acid (2.5 mmol) and sodium hydrox- ide (10 ml, 0.1 N) in distilled water was added to a magnetically stirred methanolic solution of lead nitrate (2 mmol). The reaction mixture was stirred for 2 h at room temperature. The white polycrystalline product
was filtered, washed with distilled water and dried at 110◦C for 2 h. The solid product was calcinized at 500◦C for 2 h. Over the course of this process, the white PbO nanoparticles turned pale yellow colour.
2.2 Synthesis of tetrahydro benzo pyran derivatives A mixture of aromatic aldehydes (1 mmol), malononi- trile (1 mmol), dimedone (1 mmol) and PbO nanoparti- cles (50 mg) were ground at a room temperature with a mortar and pestle. The reaction was monitored by thin- layer chromatography (TLC). After completion of reac- tion, the product was washed with distilled water. The crude product was dried and recrystallized from ethanol to afford pure compounds with high yield (table 1;
scheme1).
2.3 Spectroscopic data
2.3a Compound (table1, 4a): IR (KBr, cm−1): 3392, 3319, 3182, 2954, 2192, 1681, 1656, 1360 cm.−1 1H NMR (400 MHz, DMSO-d6): 0.94 (s, 3H, CH3), 1.04 (s, 3H, CH3), 2.08 (d, J= 16.0 Hz, 1H), 2.23 (d, J = 16.0 Hz, 1H), 2.50 (m, 2H, CH2), 4.11 (s, 1H), 7.06 (s,
Table 1. PbO nanoparticles catalysed synthesis of tetrahydro benzo pyrans.
Entry Product (R group) Time (min) Yield (%) M. P. (◦C) observed (reported)ref.
4a H 15 83 229 (227–229)14
4b 4-Cl 12 90 212 (212–214)14
4c 4-OMe 18 85 201 (201–203)14
4d 2-Cl 15 86 202 (200–202)12
4e 4-NO2 10 91 180 (178–180)14
4f 4-OH 15 82 208 (206–208)10
4g 3-NO2 15 85 212 (210–212)14
4h 3-OH 15 81 236 (236–238)10
4i 2-Furyl 20 85 198 (196–198)21
4j 2-Thienyl 20 83 211 (210–212)21
All the products are known compounds and were identified by comparison of their melting points and spectral data those with reported10,12–14,21
CHO
CN CN
O
O O
CN
NH2 O
R
R
PbO Nanoparticles Grinding
Scheme 1. Synthesis of tetrahydro benzo pyrans.
Table 2. PbO nanoparticles catalysed synthesis of benzylidene malonitriles.
Entry Product (R group) Time (min) Yield (%) M. P. (◦C) observed (reported)ref.
3a H 09 91 88 (87–88)28
3b 4-OMe 13 92 115 (115–116)26
3c 3-NO2 19 95 102 (102–103)26
3d 4-OH 25 93 185 (185–186)26
3e 4-NO2 09 96 160 (159–160)26
3f 2-Cl 26 90 94 (94–96)26
3g 4-Cl 13 92 162 (162–163)28
3h 2-NO2 18 90 139 (138–139)25
All the products are known compounds and were identified by comparison of their melting points and spectral data with those reported25,26,28
br, 2H, NH2), 7.19 (m, 3H, ArH), 7.33 (m, 2H). MS (m/z)=294 (M+1).
2.3b Compound (table 1, 4b): IR (KBr, cm−1): 3303, 3041, 2994, 2246, 1653, 1613, 1490, 850 cm.−1
1H NMR (400 MHz, DMSO-d6): 1.07 (s, 3H, CH3), 1.12 (s, 3H, CH3), 2.26 (s, 2H, CH2), 2.46–2.48 (m, 2H, CH2), 4.43 (s, 1H, CH), 6.58 (s, 2H, NH2), 7.18–7.28 (m, 4H, ArH). MS (m/z)=328 (M+1).
2.3c Compound (table1, 4c): IR (KBr, cm−1): 3400, 3300, 3040, 2990, 2240, 1680, 1510, 840 cm.−1 1H NMR (400 MHz, DMSO-d6): 1.03 (s, 3H, CH3), 1.11 (s, 3H, CH3), 2.21 (d, J =16.0 Hz, 1H), 2.22 (d, J = 16.0 Hz, 1H), 2.43 (s, 2H), 3.77 (s, 3H), 4.36 (s, 3H), 4.55 (s, 2H), 6.84 (d, J = 8.7 Hz, 2H), 7.15 (d, J = 8.7 Hz, 2H). MS (m/z)=324 (M+1).
2.3d Compound (table1, 4e): IR (KBr, cm−1): 3394, 3323, 3213, 2970, 2193, 1683, 1523, 1365 cm.−1 1H NMR (400 MHz, DMSO-d6): 0.99 (s, 3H, CH3), 1.06 (s, 3H, CH3), 2.14 (d, J =16.0 Hz, 1H), 2.30 (d, J = 16.0 Hz, 1H), 2.53–2.57 (m, 2H, CH2), 4.39 (s, 1H), 7.24 (s, 2H, NH2), 7.48 (d, 2H, J=8.4 Hz, ArH), 8.21 (s, J=8.4 Hz, 2H, ArH). MS (m/z)=339 (M+1).
2.4 Synthesis of benzylidene malonitrile derivatives (scheme2)
A mixture of aromatic aldehydes (1 mmol), malono- nitrile (1 mmol) and PbO nanoparticles (40 mg) was ground in the presence of sunlight at room temperature.
The reaction was monitored by TLC. After completion of reaction, the crude product was washed with distilled water, dried and recrystallized from alcohol to afford pure product (table2).
2.5 Spectroscopic data
2.5a Compound (table2, 3c): IR (KBr, cm−1): 3107, 2225, 1945, 1610, 1595, 1529, 1479 cm.−1 1H NMR (400 MHz, DMSO-d6): 7.86 (s, 1H), 8.31 (s, 1H, = CH), 8.33–8.45 (m, 3H). MS (m/z)=200 (M+1).
2.5b Compound (table 2, 3d): IR (KBr, cm−1): 3350, 3026, 2223, 1569, 1511 cm.−1 1H NMR (400 MHz, DMSO-d6): 6.91 (d, J=6.4 Hz, 2H, ArH), 7.89 (s, 2H, ArH), 7.97 (s, 1H,=CH). MS (m/z)=171 (M+1).
2.5c Compound (table2, 3e): IR (KBr, cm−1): 2231, 1607 cm.−1 1H NMR (400 MHz, DMSO-d6): 8.12 (d, 2H, J=8.8 Hz, ArH), 8.31 (d, J =8.8 Hz, 2H, ArH), 8.50 (s, 1H,=CH). MS (m/z)=200 (M+1).
2.5d Compound (table 2, 3g): IR (KBr, cm−1): 2229, 1584 cm.−1 1H NMR (400 MHz, DMSO-d6): 7.51 (d, 2H, J=8.5 Hz, ArH), 7.70 (s, 1H,=CH), 7.85 (d, 2H, J=8.5 Hz, ArH). MS (m/z)=189 (M+1).
Figure 1. FTIR spectrum of nanocrystalline PbO catalyst.
CHO
CN CN R
PbO nanoparticle R.T. grinding
1 2 3 (a-h)
CN CN
R
Scheme 2. Synthesis of benzylidene malonitriles.
3. Results and discussion
The FT-IR spectra of PbO nanoparticles show bands at 574, 642 and 844 cm−1 due to Pb–O vibrations (figure 1). The absorption band around 3400 cm−1 is due to the presence of water molecules. The XRD pattern (figure 2) suggests that the PbO nanoparticles contain 111, 002, 200, 210, 022, 222, 311 and 131 crys- tal planes. XRD pattern of the synthesized PbO con- firmed the formation of a single orthorhombic struc- ture (JCPDS Card No. 76–1796) with space group Pca 21 (29). Sharp diffraction peaks indicated good crys- tallinity. The broadening of peaks indicated that the particles are in nano regime and are in good agree- ment with observed SEM images. The average parti- cle size of PbO nanoparticles was determined using Debye–Scherer formula41and was found to be 69 nm.
The SEM image (figure3) showed the morphology and size of the synthesized PbO nanoparticles which, suggested the surface of the PbO nanoparticles are spongy and discrete in appearance. The elemental ana- lysis (EDAX) confirmed the material contain Pb and O elements (figure 4). The TEM image revealed that the synthesized PbO material is orthorhombic with several hexagonal shaped crystallites (figure5). The dark spot in the TEM micrograph (figure 5) can be alluded to
Figure 2. XRD pattern of nanocrystalline PbO catalyst.
Figure 3. SEM image of nanocrystalline PbO catalyst.
synthesized PbO nanoparticles as SAED pattern associ- ated with such spots reveals occurrence of PbO in total agreement with the XRD data. The average size of the PbO nanocrystallite by TEM was found to be 69 nm.
The N2 adsorption–desorption isotherms and BJH pore size distribution of PbO nanoparticles (figure 6) revealed that the samples have typical IV N2 adsorption–desorption isotherms with H1 hysteresis which indicated that the sample reserve the cylin- drical mesopores. The BJH pore size distribution demonstrated that all the samples have a narrow pore diameter range. Based on the N2 adsorption–
desorption isotherms, the specific surface area (SBET) of PbO nanoparticles obtained from BET method was 31.99 m2/g, the average pore volume (VP) and pore diameter (dp) were 0.02256 cc/g and 30.86 Å (figure6).
Figure 4. EDAX spectrum of nanocrystalline PbO catalyst.
Figure 5. (a) TEM image of nanocrystalline PbO catalyst.
(b) SAED image of nanocrystalline PbO catalyst.
3.1 Catalytic results
In continuation of our work on the synthesis of hetero- cyclic molecules using nanoparticles for cyclization and condensation reactions.42,43 We report here facile syn- thesis of tetrahydrobenzo pyrans and benzylidene malo- nitriles by grinding under solvent-free condition using PbO nanoparticles. To optimize the reaction condition for synthesis of tetrahydrobenzopyrans, benzaldehyde, malononitrile and dimedone were used as a reactant.
Figure 6. BET surface area and pore size of nanocrys- talline PbO catalyst.
In order to verify the role of grinding, the reaction mixture was left over night when it was observed that reaction remained incomplete and in the absence of cat- alyst does not proceed even after grinding. Under the optimized reaction conditions, a range of substituted tetrahydrobenzo pyran derivatives were synthesized by grinding at room temperature (table 1) using PbO as catalyst. In order to study the scope of the reaction, several substituted aromatic aldehydes with electron- donating as well as electron-withdrawing groups were employed. The reaction proceeded smoothly with good yields. The aromatic aldehydes with hydroxyl group required longer reaction time and gave lower yield. The heterocyclic aldehydes also reacted smoothly to give corresponding derivatives.
Similarly, for the synthesis of benzylidene maloni- triles, benzaldehyde and malononitrile were used as model reaction to optimize the reaction condition. As mentioned above, the role of grinding was important for completeness of reaction. Under the optimized reaction conditions a range of substituted benzyli- dene malonitrile derivatives were synthesized by grin- ding at room temperature (table 2). The reactions proceeded smoothly for electron-withdrawing and electron-donating aromatic aldehydes with high yields.
The aromatic aldehydes with hydroxyl groups and chloro groups at ortho position required longer reac- tion time and gave lower yields. The strong electron- donating aromatic aldehydes reacted quickly with high yields.
Table 3. Effect of amount of catalyst on the reaction.
Scheme1a Scheme2b Catalyst Time Yield Time Yield
Entry (mg) (min) (%) (min) (%)
1 10 40 61 21 76
2 20 32 63 16 81
3 30 21 75 12 87
4 40 17 81 07 91
5 50 12 83 07 91
6 60 12 83 07 90
7 70 12 83 07 90
aBenzaldehyde (1.0 mmol), malononitrile (1.0 mmol), dime- done (1.0 mmol) in the presence of catalyst
bBenzaldehyde (1.0 mmol), malononitrile (1.0 mmol) in the presence of catalyst
The role of catalyst was also studied for the model reaction with different amount of catalysts such as 10, 20, 30, 40, 50, 60 and 70 mg. It was observed that 50 mg of catalyst was sufficient to promote the reaction and greater amount of the catalyst did not improve the yields (table3). In the synthesis of benzylidene malono- nitriles, to study the amount of catalyst required, the model reaction of benzaldehyde and malononitrile (scheme2) was used with different amount of catalysts such as 10, 20, 30, 40, 50, 60 and 70 mg. It was found that the use of 40 mg of the catalyst was sufficient to promote the reaction (table3).
To study the reusability of catalyst, it was separated after the completion of the reaction, washed with ace- tone and dried at 100◦C and reused in the model reac- tion for four consecutive runs (table 4). Further, recy- cled catalyst was characterized by different analytical techniques. We observed that the particle size and crystal morphology of reused PbO nanoparticles was nearly the same. After every use, a little loss of cata- lytic activity was observed which may be attributed to microscopic change in the structure of the catalyst.
Table 4. Recycling of catalyst.
1 2 3 4 5
First Second Third Fourth Reaction Cycle Fresh reuse reuse reuse reuse
Scheme1 Yield (%) 83 81 79 79 71
Scheme2 Yield (%) 91 90 89 89 80
4. Conclusions
We have developed a convenient, efficient protocol for one-pot synthesis of tetrahydrobenzo pyrans and benzylidene malonitriles in the presence of nanocrys- talline PbO catalyst by grinding at room temperature.
The attractive features of this procedure are simple work-up, mild reaction condition, short reaction time, excellent yield, solvent-free reaction and utilization of nanoparticles as a reusable catalyst.
Supplementary material
Supplementary material given as figuresS1–S5 can be seen onlinewww.ias.ac.in/chemsciwebsite.
Acknowledgements
Authors thank the University Grants Commission (UGC), New Delhi, for financial support, University of Pune, Pune and Sophisticated Analytical Instru- ment Facility (SAIF) Panjab University, Chandigarh for providing spectral analysis facilities. Authors are also thankful to Prof. A G Gadhave for his helpful suggestions.
References
1. a) Montandon J B, Zijlstra F J and Wilson J H P 1989 Int.
J. Tissue React. 11 107; b) Brooks G T 1998 J. Pestic.
Sci. 22 41
2. a) Hafez E A A, Elnagdi M H, Elagamey A G A and EL-Taweel F M A 1987 Heterocycles 26 903; b) Abdel Galil F M, Riad B Y, Sherif S M and Elnagdi M H 1982 Chem. Let. 11(8) 1123
3. Osherov N, Gazit A, Gilon C and Levitzki A 1993 J. Bio.
Chem. 268 11134
4. Kamath S and Buolamwini J K 2003 J. Med. Chem.
46(22) 4657
5. Li R, Pourpak A and Morris S W 2010 J. Med. Chem.
52(16) 4981
6. Lee C T, Adachi Y and Carbone D P 2005 Gene. Ther.
Mol. Biol. 9 77
7. Pore D M, Undale K A and Dongare B B 2009 Catal.
Lett. 132(1–2) 104
8. Katkar S S, Lande M K, Arbad B R and Gaikwad S T 2011 Chin. J. Chem. 29(1) 199
9. Islami D M and Mosaddegh E 2009 Phosphorus Sulfur Silicon Related Elem. 184(12) 3134
10. Balalaie S, Bararjanian M, Amani A M and Movassagh B 2006 Synlett 2 263
11. Oskooie H A, Heravi M M, Karimi N and Zadeh M E 2011 Synth. Commun. 41(3) 436
12. Jin T S, Wang A Q, Wang X, Zhang J S and Li T S 2004 Synlett 5 871
13. a) Ziarani G M, Abbasi A, Badiei A and Aslani Z 2011 E-J. Chem. 8(1) 293; b) Bahareh S, Alireza H and Somayeh B 2011 J. Chem. Res. 35(11) 666
14. a) Gurumurthi S, Sundari V and Vallippan R 2009 E-J.
Chem. 6(S1) S 466; b) Mobinikhaledi A and Fard M A 2010 Acta. Chim. Slov. 57 931
15. a) Wang L M, Shao J H, Tian H, Wang Y H and Liu B 2006 J. Fluorine Chem. 127 97; b) Mei H and Chun C 2010 J. Chem. Res. 34(10) 568
16. Zhao L, Li Y, Chen L and Zhou B 2010 J. Org. Chem.
30(1) 124
17. Nemouchi S, Boulcina R, Carboni B and Debache A 2012 Comptes Rendus Chime. 15(5) 394
18. a) Saini A, Kumar S and Sandhu J S 2006 Synlett 12 1928; b) Sun W B, Zhang P, Fan J, Chen S H and Zhang Z H 2010 Synth. Commun. 10(4) 587
19. Balaskar R, Gavade S, Mane M, Pabrekar P, Shingare M and Mane D 2011 Lett. Org. Chem. 8(4) 282
20. Feng C, Wang Q, Lu C, Yang G and Chen Z 2012 Com- binatorial Chem. High Throughput Screening 15(1) 100 21. Ranu B C, Banerjee S and Roy S 2008 Indian J. Chem.
47B 1108
22. Yu L Q, Liu F and You Q D 2009 Org. Prep. Proc. Int.
41 77
23. a) Balalaie S, Bararjanian M, Ahmadi M S, Hekmat S and Salehi P 2007 Synth. Commun. 37(7) 1097; b) Abdolmohammadi S and Balalaie S 2007 Tetrahedron Lett. 48 3299
24. Peng Y and Song G 2003 Indian J. Chem. 42B 924 25. Shi D Q, Chen J, Zhuang Q Y, Wang X S and Hu H W
2003 Chin. Chem. Lett. 14(12) 1242
26. Ye W, Jiang H and Yang X C 2011 J. Chem. Sci.
123(3) 331
27. Parida K M, Rath D and Mol J 2009 J. Mol. Catal. A:
Chem. 310 93
28. Mogilaiah K, Babu S H, Vidya K and Kumar K S 2010 Indian J. Chem. 49B 390
29. Abaee M S, Mojtahedi M M, Zahedi M M and Khanalizadeh G 2006 Arkivoc xv 48
30. a) Cardillo G, Fabbrani S, Gentilucci L, Gianotti M and Tolomelli A 2003 Synth. Commun. 33 1587; b) Wang Y, Shang Z, Wu T, Fan J and Chen X J 2006 J. Mol. Catal.
A: Chem. 253 212
31. a) Wang S, Ren Z, Cao W and Tong W 2001 Synth. Com- mun. 31 673; b) Jin T S, Wang X, Liu L B and Li T S 2006 J. Chem. Res. 6 346
32. Heravi M M, Bakhtiari K, Taheri and Oskooie H A 2007 J. Chin. Chem. Soc. 54 1557
33. Su F, Antonietti M and Wang X 2012 Catal. Sci. Tech- nol. 2 1005
34. Mondal J, Modak A and Bhaumik A 2011 J. Mol. Catal.
A: Chem. 335(1–2) 236
35. Reddy B M, Patil M K, Rao K N and Reddy G K 2006 J. Mol. Catal. A: Chem. 258(1–2) 302
36. Isobe K, Hoshi T, Suzuki T and Hagiwara H 2005 Mol.
Divers. 9(4) 317
37. Yuan S, Li Z and Xu L 2012 Res. Chem. Intermed.
38(2) 393
38. Kumar B V, Naik H S, Girija D and Kumar B V 2011 J.
Chem. Sci. 123(5) 615
39. Pasha S K, Satyanarayana V S V, Sivakumar A, Chidambaram K and Kennedy L J 2011 Chin. Chem.
Lett. 22(8) 891
40. Bytyn W and Baerns M 1986 Appl. Catal. 28 199 41. Dash P K and Balto Y 2011 Res. J. Nanosci. Nanotech-
nol. 1 25
42. Borhade A V, Tope D R and Patil D R 2012 Res. Chem.
Intermed. doi:10.1007/s11164-012-0693-8
43. Borhade A V, Tope D R and Patil D R 2012 J. Chem.
Pharm. Res. 4(5) 2501
